The present embodiments relate to creating a resultant image based on at least two image data records.
Ever more frequent use is being made of imaging x-ray devices (e.g., a C-arm x-ray device or a computed tomography device) for the resolution of medical issues. What imaging x-ray devices have in common is that imaging x-ray devices have an x-ray source (e.g., an x-ray tube), as well as an x-ray detector interacting with the x-ray source. The x-ray radiation emitted by the x-ray source passes through a patient to be examined and is attenuated by interacting with the different tissue types of the patient. The detector is disposed beyond the patient in relation to the x-ray source, accepts the remaining x-ray radiation beyond the patient, and converts the x-ray radiation into the electrical signals corresponding to the x-ray attenuation caused by the patient.
The x-ray source emits x-ray radiation with one emission spectrum, which provides that the gamma quanta emitted by the x-ray source have an energy distribution including a plurality of quanta energy values. In other words, the x-ray source emits polychromatic x-ray radiation. The emission spectrum is decisively influenced by the x-ray tube voltage or the acceleration voltage with which the x-ray source is operated. In general terms, the higher the acceleration voltage is, the greater the average x-ray quanta energy of the emission spectrum also is.
It is known that different materials or tissue types (e.g., water or bones) interact with x-ray radiation to different degrees. Expressed in simpler terms, the image contrast in all x-ray images is based on these differences. The energy dependence of the x-ray attenuation on passage through material is also known. This provides that low-energy x-ray radiation is absorbed more strongly by material than higher-energy x-ray radiation.
These differences in the interaction between x-ray radiation and material is to be taken into account during x-ray imaging in order to create x-ray images that have sufficient image quality to respond to the medical issue and protect the patient from an unnecessary dose load.
The acceleration voltage may be set for this purpose before an x-ray image is recorded. The decisive factors in the choice of a suitable acceleration voltage are the underlying medical issue, the image quality to be achieved, a reduction of the patient dose, or the amount of contrast medium to be administered for the x-ray and/or individual x-ray attenuation characteristics of a patient. Thus, low acceleration voltages ranging from 70 kV to 100 kV may be used for the x-ray image recording while administering contrast media containing iodine in order to optimize the iodine contrast-to-noise ratio with a low dose, while higher acceleration voltages, such as around 140 kV, are then employed, for example, if instead there are likely to be strong metal artifacts in the x-ray images.
Until now, the user (e.g., a doctor or a medical specialist) has set the acceleration voltage manually. For this purpose, modern x-ray imaging devices have automatic dosing systems available to them, with the aid of which the acceleration voltage is set automatically or semi-automatically for an x-ray scan or an x-ray image. In such cases, the automatic dosing system offers the user a choice of acceleration voltages in the definition of the scan protocol (e.g., 70 kV, 80 kV, 100 kV, 120 kV and 140 kV), from which a selection of the optimum acceleration voltage is made as a function of the planned examination, the anatomical circumstances of the patient, the image quality, and/or characteristics of the x-ray imaging device. As an alternative, the automatic dosing system just shows the user a corresponding suggestion for the optimum acceleration voltage for confirmation or sets the optimum acceleration voltage automatically.
Accordingly, imaging x-ray devices have previously had to be embodied such that the imaging x-ray devices are able to be operated with a number of different acceleration voltages. In other words, the ability to set the acceleration voltage on the part of the generator and also the x-ray source is to be provided, the x-ray tube voltage is to be able to be adapted to the optimum acceleration voltage with a constant output, and the different acceleration voltages are to be calibrated, which provides a greater technical outlay. The setting of the x-ray tube voltage on the part of the user is complex and thereby prone to errors.